The use of certain gases as sterilizing agents as bactericides, viricides and sporicides, is known. Chlorine dioxide (ClO2) is one such agent and is used annually in the U.S. at a rate of approximately 4 million pounds per year, primarily for water purification as a replacement for chlorine/hypochlorite (bleach). Chlorine dioxide is an effective microbicide as a gas and in solution and also can destroy certain chemical substances and toxins. For example, U.S. Pat. Nos. 4,504,442 and 4,681,739 to Rosenblatt et al. disclose the use of chlorine dioxide gas as a chemosterilizing agent.
In addition chlorine dioxide has excellent environmental qualities, as it does not produce large quantities of chlorinated hydrocarbon byproducts. Although large-scale production of chlorine dioxide is handled effectively by chemical generator systems, typically being track mounted when portability is needed, small-scale production is more challenging. In particular, on-demand production, rapid deployment, and portability for use in personal protection are difficult to combine in a single product.
Many processes are known for the production of ClO2 in gas or solution forms suitable for large-scale use. Success in the use of ClO2 for domestic anthrax clean-up has amply demonstrated this point for cases where a significant amount of time is available to transport heavy equipment and chemicals to the contamination site. Usually, the sophisticated equipment needed to produce ClO2 requires ample power, particularly if electrolysis is used for generation.
On the other hand, portable ClO2 dispensers for immediate decontamination that could be carried by a person and used in small areas (offices, labs, clinics, etc) or transported on vehicles are not generally available. A viable working requirement is that the dispenser should be the size and function that can be easily handled by a single individual. For example the dispenser can have the form of and function similarly to a typical fire extinguisher and preferably would require no external power and work by simply opening a valve to release a decontaminant fluid with essentially no time delay. A reasonable target is the production of 1 L of decontaminant fluid with greater than 5 mM ClO2 in less than 1 minute for such a portable dispenser. Furthermore, larger devices that could be portable by vehicle or dolly could also provide for immediate decontamination over larger areas, and small devices could provide personal decontamination of remote water supplies.
Moreover, chlorine dioxide solutions (chlorous oxide) in any form are highly unstable, so it is necessary to generate the solution immediately before use. Accordingly, the reaction components which when mixed together produce chlorine dioxide gas must be maintained separately until gas production is desired.
In general, chlorine dioxide solutions can be produced by treatment of chlorite salt solutions (e.g. NaClO2) with an acid solution to produce acidic solutions that contain ClO2. The ClO2 can be used in these solutions or flushed as a gas into water to produce aqueous ClO2. It is difficult to use this traditional approach to design, for example, a portable sprayer that can be used to treat surfaces infected by anthrax or other biological contaminants.
U.S. Patent Application Publication Nos. 20040241065 and 2004062680 to Kampa disclose on-demand chlorine dioxide generators, which can be portable. Kampa discloses a chlorine dioxide gas generating kit including a gas generating apparatus having a first reaction component contained therein and a second reaction component contained therein. The first and second reaction components are separated within the apparatus by at least one rupturable membrane. To activate the apparatus, the membrane is ruptured to permit contact between the first and second reaction components to facilitate a chemical reaction therebetween, which produces the chlorine dioxide gas.
The reaction components disclosed by Kampa are both liquid reagents. Liquid reagents risk leakage and require relatively large storage volumes. Moreover, chlorine dioxide production according to Kampa requires the rupture a rupturable membrane to permit contact between the reagents. Rupture of the membrane can occur inadvertently during handling or even prevent dispensing when desired. Significantly, the required rupture provides only one-shot use where the entire first reaction component is mixed with the entire second reaction component upon rupture of the membrane.
Ion exchange mediums are known for the formation of chlorous oxide. For example, U.S. Pat. No. 3,684,437 to Callerame discloses production of chlorous oxide by ion exchange between a mixed bead cation-anion exchange resin and a chlorite of an alkali metal or an alkaline earth metal with a flow rate of 1 mL/minute or less. Heating the solution formed by the ion exchange reaction liberates gaseous chlorine dioxide. Similarly, U.S. Patent Application Publication Nos. 20030064018 and 20050196337, both to Sampson et al. disclose generation of chlorous acid from a chlorite salt precursor, a chlorate salt precursor, or a combination of both by passing an aqueous solution of the precursor through a cationic ion exchange resin in a hydrogen ion form and a catalytic material to accelerate the decomposition of chlorous acid to chlorine dioxide using gravity feed and a flow rate of 30 mL/minute. Both Callerame and Sampson disclose only bulk or laboratory methods for forming chlorous oxide, with no adaptability for on-demand or portable chlorous oxide generation, where flow rates of approximately 1 L/minute or more are needed.